Active addressing of passive matrix displays

In May of 1992, T. Scheffer and B. Clifton of In Focus Systems reported on a new method to eliminate frame response in passive matrix LCDs that did not require the costly transistors of an active matrix display. Dubbed Active Addressing, this technology has been shown to be successful in achieving high contrast ratios and fast response displays rivaling the quality of active matrix, but with a cost of manufacturing closer to that of passive matrix. Active Addressing relies upon the proven low cost manufacturing techniques associated with passive matrix LCDs and adds external electronics that changes the standard addressing wave forms such that frame response can be avoided. Specifically, instead of the simplistic one row at a time addressing method currently used, it was shown that a wide variety of orthonormal functions can be used to allow many rows to be selected simultaneously. In such a system a calculation must be made based upon the desired image data and the specific row function to be presented to the display resulting in complex column voltages. However, once this calculation is made and these column and row signals are presented to the display, each pixel will now receive many small pulses throughout the frame instead of the one large pulse and a long dead time associated with standard passive matrix addressing. In this way, a near constant voltage is applied to each pixel very similar to that of an active matrix display, thus eliminating frame response and allowing the passive matrix display to be constructed using very fast responding liquid crystal material.<
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